This invention relates generally to radiation detectors and, more specifically, to a suspension and protection system for portal monitoring radiation detectors.
Existing portal monitoring radiation detectors are often subjected to varying degrees of shock or vibration during normal usage. In some cases, the degree of shock or vibration exposure may be quite severe. Deleterious effects from shock and vibration may include high background counts, noise in the detector's response spectrum, and even breakage of the detector.
Existing shock and vibration isolation systems for radiation detectors typically consist of either an elastomeric boot that is telescoped over the radiation detector, or a foam pad that is wrapped around the radiation detector. Due to size constraints in portal monitoring radiation detectors, these methods are commonly not even attempted. In many cases, the crystal component of the detector is simply wrapped in a reflective material and then inserted into a 1 mm thick stainless steel housing. A typical crystal component is in the shape of a 2″×4″ rectangle that is 16″ long. It may be in other shapes, however, one common variation being a 4″×4″ square that is also 16″ long. These rectangular and square crystal components are then commonly coupled to a photomultiplier tube (PMT). Typical portal monitoring radiation detectors use round PMTs that are easily obtained and tend to have uniform resolution independent of where light interacts with the photocathode. The crystal is coupled to the round PMT with a pseudo rounded-rectangular light pipe that has an efficiency of approximately 65% based on an 8″ square inch surface area for the crystal being exposed to approximately 65% of the PMT surface area (for a 3″ round PMT). The crystal and the PMT are commonly glued to the light pipe interface, but frequently become uncoupled, however, due to shock, vibration, temperature fluctuations, or other typical field exposures. Moreover, the stainless steel housing and any internal isolation systems that may be employed typically reduce the detector's effectiveness to measure gamma radiation at low energy levels due to their attenuating effects.
Finally, the light pipes and photomultiplier tubes (PMTs) used in these types of detectors are not optimized for light transmission and collection.